1. Field of the Invention
The present invention relates to a single headed swash plate type compressor used for an air-conditioner incorporated into a vehicle, for example.
2. Description of the Related Art
A conventional single headed swash plate type compressor is disclosed in Japanese Unexamined Patent Publication No. 11-107912. This single headed swash plate type compressor comprises a housing having cylinder bores, a crank chamber, a suction chamber and a discharge chamber, and pistons reciprocatingly arranged in the cylinder bores. A drive shaft is rotatably supported by the housing, and this drive shaft is driven by an external drive source. Further, a swash plate is supported by the drive shaft for rotation therewith, and a pair of shoes is arranged between the swash plate and the piston. That is, the piston has a body portion in slidable contact with the inner circumferential surface of the cylinder bore, and the shoes are connected between the shoe connecting portion (neck portion), which is integrally formed with the body portion, and the swash plate. In this single headed swash plate type compressor, a stroke of the piston and an inclination angle of the swash plate are changed according to a pressure difference between the crank chamber pressure and the suction pressure. Due to the foregoing, the discharge capacity can be controlled. The characteristic structure of the single headed swash plate type compressor, as disclosed in this publication, includes a cavity formed in the body portion of the piston to realize a reduction in weight. Here, the term xe2x80x9ccavityxe2x80x9d includes a completely closed cavity not communicating with the outside and a partially closed cavity (lightening hole) communicating with the outside via an opening such as a communicating hole.
In this single headed swash plate type compressor, when the drive shaft is driven by the external drive source, the swash plate is rotated synchronously with the drive shaft, and the pistons are reciprocated in the cylinder bores via the shoes. Due to the foregoing, since a compression chamber is formed between the cylinder bore and the piston head, when this compression chamber is in a suction stroke, refrigerant gas at low pressure is sucked into the compression chamber from the suction chamber connected with an evaporator provided in the refrigerating circuit, and when this compression chamber is in a compression stroke, refrigerant gas at high pressure is discharged from the compression chamber into a discharge chamber. The discharge chamber is connected with a condenser provided in the refrigerating circuit. In this way, the refrigerating circuit is used for an air conditioning system incorporated into a vehicle.
In the above described conventional single headed swash plate type compressor, when a cavity is formed in the piston so that the weight of the compressor can be reduced, the mechanical strength of the body portion of the piston is decreased because of the cavity. Especially when an opening, connecting the cavity in the piston with the outside, is formed, there is a possibility that the mechanical strength of a portion of the piston close to the opening becomes insufficient.
It is an object of the present invention to provide a single headed swash plate type compressor in which, while utilizing the advantages of forming a cavity in the piston, durability of the compressor is enhanced even when it is operated under a severe operating condition.
The present invention provides a single headed swash plate type compressor comprising: a housing having cylinder bores, a crank chamber, a suction chamber and a discharge chamber formed therein; pistons reciprocatingly arranged in the cylinder bores, each piston having a body portion slidably fitted in the cylinder bore and a neck portion connected to the cylinder bore; a drive shaft rotatably supported by the housing; a swash plate arranged in the crank chamber and supported by the drive shaft for rotation therewith, the swash plate being operatively connected to the neck portions of the pistons to move the pistons; the body portion of the piston having a cavity formed therein to reduce the weight of the piston; and the piston having at least one rib to reinforce the body portion.
In the single headed swash plate type compressor of the present invention, the cavity is formed in the body portion of the piston, so the weight of the compressor can be reduced. The cavity may be either a partially closed cavity or a completely closed cavity. In the single headed swash plate type compressor of the present invention, the piston has at least one rib, which reinforces the body portion of the piston. This rib may be located either outside or inside the cavity.
Accordingly, in the single headed swash plate type compressor of the present invention, while realizing a reduction in the weight, which is an advantage of forming the cavity in the piston, durability can be enhanced even if the compressor is operated under a severe operating condition.
In the single headed swash plate type compressor according to the present invention, it is preferable that a pair of shoes are arranged between the piston and the swash plate and that the piston has at least one rib in a portion close to the neck portion of the piston for connecting the shoes. Due to the above structure, it is possible to provide a higher effect of reinforcing the body portion. That is, in the suction or compression stroke, a portion close to the shoe connecting section of the piston mostly receives compression stress, an inertial force and a bending moment. Therefore, it is most effective to arrange the rib in the portion close to the shoe connecting portion.
In the single headed swash plate type compressor according to the present invention, it is preferable that the cavity has openings which open at positions on either side of the neck portion of the piston, and the rib is formed between both the openings. In this arrangement, no burr is left in the cavity in the manufacturing process and welding conducted in vacuum is avoided so that manufacturing can be simply performed. In this structure, a portion between both the openings tends to become relatively fragile, however, when the rib is provided here, it becomes possible to ensure a sufficiently high mechanical strength.